Recently, inhibition of the endolysosomal system has been described among the earliest changes in Alzheimer?s disease (AD) brains and may contribute to the well-known hallmarks: formation and buildup of amyloid and Tau tangles. Our recently published studies show that in early onset familial AD and late onset sporadic AD nuclear activity of the transcription factor EB (TFEB) and consequently many of the cellular clearance mechanisms are greatly attenuated. Our preliminary studies presented in this proposal identify the TFEB-target gene, Mucolipin (MCOLN1), as the central regulator of endolysosomal trafficking and clearance in AD human brains, cultured human neurons, and a mouse model of the disease. MCOLN1 are endolysosomal calcium release channels playing central roles in the regulation of the TFEB signaling, organelle fusion, exocytosis, and trafficking. We find that endolysosomes carrying APP, BACE1 and A? contain low levels of MCOLN1, fail to tether to Dynein, and accumulate in neuronal projections in postmortem human brains and cultured neurons from AD patients. We observe that reactivation or overexpression of MCOLN1 in cultured human AD neurons and 5xFAD mice promotes retrograde trafficking and clearance of A?-positive endolysosomes from the presynaptic terminals and fibrillary A? from the extracellular space, consequently leading to an improvement of memory function. We will test the overall hypothesis that MCOLN1 drives endolysosomal trafficking to maintain neural clearance and its deregulation results in the known Alzheimer?s disease hallmarks including A? deposition and memory loss. Our molecular sensors, tools, human neuronal lines and transgenic mice will be used to test the overall hypothesis that MCOLN1 drives endolysosomal trafficking to maintain neural clearance and its deregulation results in the known Alzheimer?s disease hallmarks including memory loss. The overall goal of this proposal is 1) to understand the AD-specific mechanism leading to inhibition of endosomal trafficking and autophagy, and 2) to identify consequences of functional failure of neuronal clearance in AD that could facilitate future development of interventions to preserve neuronal homeostasis in aging.